Drilling column comprising a device for measuring stresses exerted on the column

ABSTRACT

A strain measuring device adapted to a drill pipe, comprising in combination a deformable member, sensitive to the action of strains applied to the pipe in at least one direction and provided with means for detecting these strains, connected to conductors for remote measuring associated to the drill pipe, a safety element capable of withstanding accidentally high values of these strains, and connecting means between said member and said element, adapted to permit a limited displacement of said deformable sensitive member in said direction with respect to said safety element, as a result of the application of the strains said sensitive member coming into abutment against said safety element, when the value of the strain in said direction exceeds a predetermined limit value.

ilnited States Patent Chatard et a1.

[54] DRILLING COLUMN COMPRISING A DEVICE FOR MEASURING STRESSES EXERTEDON THE COLUMN Aug. 29, 1972 3,439,541 4/1969 Gilder ..73/14l A FOREIGNPATENTS OR APPLICATIONS 587,096 4/1947 Great Britain ..73/l41 A 918,3382/1963 Great Britain ..73/136 A 1,122,742 1/1962 Germany .;..73/136 APrimary Examiner-Charles A. Ruehl AttorneyCraig, Antonelli and Hill [57]ABSTRACT A strain measuring device adapted to a drill pipe, comprisingin combination a deformable member, sensitive to the action of strainsapplied to the pipe in at least one direction and provided with meansfor detecting these strains, connected to conductors for remotemeasuring associated to the drill pipe, a safety element capable ofwithstanding accidentally high values of these strains, and connectingmeans between said member and said element, adapted to permit a limiteddisplacement of said deformable sensitive member in said direction withrespect to said safety element, as a result of the application of thestrains said sensitive member coming into abutment against said safetyelement, when the value of the strain in said direction exceeds apredetermined limit value.

5 Claims, 11 Drawing Figures [72] Inventors: Michel Chatard, Chatou;Remi Reynard, Montesson, both of France [73] Assignee: Institut Francaisdue Petrole, des

Carburants et Lubrifiants, Rueil- Malmaison (Hauts de Seine), France[22] Filed: April 20, 1970 [21] Appl.No.: 30,086

[52] US. Cl. ..73/151, 73/88.5 R [51] Int. Cl. ..E21b 47/00 [58] Fieldof Search ..73/88.5 R,133, 141 A, 151, 73/136 A [56] References CitedUNITED STATES PATENTS 2,775,887 1/1957 Hines ..73/l4l A 2,795,134 6/1957Weber et a1. ..73/141 A 2,877,646 3/1959 Dudenhausen ..73/141 A3,376,921 4/1968 Manry etal ..73/15l X amam Patented Aug. 29, 1972 FIGZB3 Sheets-Sheet l INVENTORS NlCHEL CHATAR and REM! REYNARD AITORNEYSPatented Aug. 29, 1972 3 Sheets-Sheet 2 FIG5 FIGSA FIG 4 FIG 4A [NVENTORS MlCHEL CHATARDauol REMt REYNARD ATI'O RNEYS DRILLING COLUMNCOMPRISING A DEVICE FOR MEASURING STRESSES EXERTED ON THE COLUMN Thepresent invention relates to a device for remotely controlling andmeasuring the strains exerted on a drill pipe.

This device is suitable for remotely measuring strains due to tractiveand bending forces, as well as those resulting from torques exerted onthe drill pipe.

The remote measuring of the strains applied to a drill pipe can beeffected by placing on this pipe, or more generally on a support memberintegral therewith, strain sensitive devices such as strain gauges.

Unfortunately, the sensitivity of such a detecting system is notsufficient unless the element whereon the strain gauges are located isdeformable enough in operation, under the action of the applied strains.

This aptitude to deformation which can be obtained by a suitableselection of the material constituting the support member at the placewhere the strain gauges are located, and by a reduction of itscross-section, is a requirement which is often hardly compatible withthe requirement of a sufficient mechanical strength of this deformablemember, this mechanical strength being absolutely necessary since thiselement is a part of a drill pipe subjected to high strains and itsbreaking could have serious consequences.

The main object of the invention is accordingly to provide a deviceadapted to a drill pipe and exhibiting both a high sensitivity relativeto the action of the strains and a mechanical strength which issufficient for withstanding quite safely a high accidental increase inthese strains.

This object is achieved, according to the invention, with a strainmeasuring device comprising in combination a deformable member connectedto the drill pipe, said member being sensitive to strains applied to thepipe along at least one direction and being provided with means fordetecting these strains, connected to conductors for remote measuring,associated with the drill pipe, a safety element capable of withstandingaccidentally high values of these strains and connecting means betweensaid deformable member and said safety element, adapted to provide for alimited displacement of said sensitive member in said direction,relative to said safety element, as a result of a deformation of saidsensitive member due to the effect of the strains, said sensitive membercoming into abutment against said safety element when the value of thestrain along said direction becomes greater than a predetermined value.

Said connecting means may for example comprise at least one pinconnecting said sensitive member and said safety element and limitingthe displacement of said sensitive member and/or said safety element,relative to said pin.

In another embodiment said sensitive member and safety element will beconnecting by screwing, using two complementary threadings allowing alimited relative displacement of said sensitive member and safetyelement in at least one direction, under the action of strains appliedto the sensitive member.

The sensitive member and the safety element will advantageously consistof two coaxial tubular elements, respectively connected to the upper andthe lower sections of the pipe, the safety element being preferablyplaced around the sensitive member, so that the wall thickness of thesafety element, which is greater than that of the sensitive member, donot result in a reduction of the passage cross-section provided for theflow of drilling fluid through the pipe, at the place of location of theremote measuring device.

Some non-limitative embodiments of the invention are describedhereinunder with reference to the appended drawings, wherein:

FIG. 1 illustrates a first embodiment of the invention,

FIG. 2 shows the position of a pin connecting the safety element and thesensitive member for the value zero of the strain applied to the latter,

FIG. 2A shows a connecting pin in abutment against the safety elementwhen the traction strain reaches a predetermined limit,

FIG. 2B shows similarly the limit position of a connecting pin when thetorque becomes greater than a selected value,

FIG. 3 illustrates an alternative embodiment for the device of FIG. 1

FIGS. 4 and 4A are relative to this alternative embodiment andillustrate an arrangement similar to that shown in FIGS. 2 and 213respectively,

FIGS. 5 and 5A illustrate other means for providing a relative axialplay between the sensitive member and the safety element of the device,and

FIGS. 6 and 6A represent schematically the arrangement of the measuringand safety elements.

Throughout the different drawings, the same reference numerals have beenused for designating a similar elements.

In FIG. 1, illustrating a first embodiment of a device for remotelymeasuring strains exerted at a point of a flexible pipe, the referencenumeral 1 designates a member adapted to be connected at its upper endto a first section of the pipe. This sensitive member consists of asleeve of small thickness and accordingly is relatively deformable underthe action of traction forces and/or torques exerted on the pipe. Thereference numeral 2 designates the safety element which consists of atube of greater wall thickness, connected to a second section of thepipe, indicated by reference numeral 3.

In this embodiment, the connecting means between the elements 1 and 2consists of pins, such as pins 4, 5 and 6, fast with the safety element5 and inserted through holes 5a, each of which offering to the pinpassing therethrough a limited play in at least one direction (the holes5a may be circular, as shown with a greater diameter than that of thepins, or ovalized in one direction).

In these conditions, the member 1 is freely deformable under the actionof strains applied to the pipe, as long as a strain in a determineddirection, due for example to a traction force (FIG. 2A) or to a torque(FIG. 2B) applied to the pipe, does not reach a fixed limit.

When this limit is reached, one at least of the pins comes into abutmentagainst the edge of a hole 5a, whose outline has been determined as afunction of the limit value permitted for the deformation of thesensitive element under the action of the strains, in each direction ofthese strains.

For example this limit will be 30 tons for the traction forces or axialloads and 400 kg.m for the torques applied to the drill pipe, thesevalues being of course indicated only by way of example.

When this limit has been reached, the safety element 2 takes up a partof the loads which beyond this limit were sustained solely by thesensitive member 1. In case of an accidental breaking of this member,the safety element would wholly sustain the loads transmitted betweenthe two pipe sections connected by the device according to theinvention.

The deformations of the sensitive member are detected by strain gaugeswhich may be of a known type, such as gauge 7 secured to the cylindricalsensitive member 1 along a generatrix thereof, this gauge beingsensitive to the axial elongation of this member, resulting fromtraction strains, and gauge 8 placed at right angles to a generatrix ofmember 1 and sensitive to a twisting of this member.

Electric signals produced by these strains gauges are transmitted,through conductors 9 and 10 respectively, to electric circuits 11 fordata or information processing, these circuits comprising in particularamplifying means which may be of a known type and transmit to the groundsurface through cable 12 all the measurements to be carried out.

In the case where the drill pipe connected to the sensitive member 1 isa flexible pipe incorporating data transmitting conductors, the cable 12may be connected to at least one of these conductors.

The electric power feeding the electric circuits 11 may be produced bybatteries or supplied through conductors (not shown in the drawing) froma surface installation at the top of the well. Conductors 13 provide forthe electric supply to other detecting devices, identical to ordifferent from the above-described detecting device and which transmitdata to the circuits 11 through cable 14.

Annular joints 22 provide for sealing between the safety element 2 andthe sensitive member 1, with respect to the drilling fluid which flowsthrough the drill pipe.

In the embodiment illustrated in FIG. 1, an external protecting sleeve15 covers the sensitive element 1 and annular joints 23 provide forsealing with respect to the drilling fluid flowing through the drillpipe and through the annular zone between the wall of the drilled welland the protective sleeve. Due to the provision of the sealing joints 22and 23, of a sufficient thickness of the safety element 2 and of theexternal protective sleeve 15, the sensitive member 1 is not subjectedto the hydrostatic pressure difference between the exterior and theinterior of the pipe and, consequently, the informations provided by thestrain gauges 7 and 8, concerning the axial load and the torque appliedto the drill pipe are not altered by this hydrostatic pressuredifference.

Pressure indicating devices 16 and 17 which measure respectively thepressure within the pipe and in the annular zone around this pipe areconnected to the electric circuits for data processing, through notshown electric conductors.

FIG. 3 wherein neither the strain gauges nor the electric conductors andcircuits are shown, illustrates an embodiment wherein the safety element2 is placed around the sensitive member 1.

An internal socket or protecting sleeve 18, provided with sealing joints22 protects the sensitive member from the contact with the drillingfluid and the safety element 1 is here again shielded from the effect ofthe hydrostatic pressure difference between the interior and theexterior of the pipe, through the safety element 2 and the externalsleeve 18, and the sealing joints 22 and 23.

This arrangement makes it possible to choose for the safety element 2any wall thickness, without being limited by the minimum section of thepassage required for the drilling fluid.

A pin 19, fast with the sensitive member 1, is inserted with someclearance through a hole 20 of the safety element 2, being adapted, asin the preceding element, to come in abutment against the edge of thishole when the torque applied to the drill pipe exceeds a predeterminedlimit value.

The sensitive member 1 and the safety element 2 are in this embodimentconnected at 21 by means of complementary threadings 21a and 21b (FIGS.5 and 5A) which are provided with some play or clearance, permitting afree extension of the sensitive member 1 under a tractive force, thismember coming however in abutment against the safety element 2 when thetractive force (having for example the direction indicated by the arrowin FIG. 5A) reaches a predetermined limit value, which depends on thetraction strength of element 1.

It results from the foregoing that the invention provides a device forremote measuring which can be made very sensitive through a reducedthickness of the member 1, while complying with the necessary safetyrequirements, in view of the presence of the element 2 which can sustainall or part of the strains applied to the pipe.

It could be possible to measure with a high accuracy values varyingwithin a wide range, by using an assembly of devices according to theinvention connected in series, so that the sensitive member 1 of one ofthese devices is connected to the safety element of an adjacent device,these devices having sensitive members of increasing thicknesses, whosedeformation would be limited, by means of pins or threadings, asabove-indicated, to respective values increasing with the thickness ofthe sensitive member, so as to prevent any risk of breaking of the mostbrittle sensitive members in the so constituted series of devicesaccording to the invention.

In FIG. 6, the measuring elements are shown at 1, 1' and 1" while thecorresponding safety elements are indicated at 2, 2 and 2". As isapparent from this figure, the measuring element 1' is connected to theadjacent safety element 2 by any known means, such as for example athread 24.

In FIG. 6A, the different safety elements have been assembled so as toconstitute only a single safety element 2 and, in like manner, themeasuring elements have been assembled in series with the aid of anyknown means so as to constitute a single measuring element 1 havingportions with a decreasing cross section.

As already indicated, a device according to the invention, adapted to adrill pipe, may be made insensitive to the difference of hydrostaticpressure between the interior and the exterior of the pipe.

However, any element located in the flow of drilling fluid, downstreamfrom the device according to the invention, such as a valve or a tubingfor turbodrilling actuated by the drilling fluid, by generating apressure drop, produces in operation a dynamic pressure increase in theflow of fluid, upstream from its location. This pressure differenceresults in an axial load applied to the pipe, which is combined with theaxial load due to parameters other than the fluid flow and whose valuehas to be measured with the device according to the invention.

A correction of the measurement carried out on the ground surface can beeasily achieved by subtracting from the measured value the quantity A Srepresenting the product of the difference A, of the values of thepressure inside the pipe respectively upstream and downstream from thelocation of the device generating the pressure drop by the useful orpassage cross-section S provided by this device to the fluid flow.

The value of S may be determined by a prior calibration, by comparingthe values indicated by the measuring device of the invention for theaxial load applied to the pipe, respectively with and withoutcirculation of drilling fluid, for a given flow rate of this fluid,before the drill bit is lowered onto the bottom of the drilled well, thevalue of the axial load applied to the sensitive member 1, in additionto the load resulting from the flow of fluid, being known and equal tothe weight of the different elements associated to the pipe (drill bit,drill collar, possibly turbine for turbo-drilling) placed below themeasuring device according to the invention.

The above-indicated correction may be carried out automatically bydevices which may be readily designed by those skilled in the art, thesedevices including means for automatic adjustment as a function of thevalue of the above-defined cross-section S.

What we claim is:

l. A drilling column consisting of portions assembled end-to-end,comprising in combination a deformable tubular measuring elementconnected at one end thereof to a first column portion and at the otherend thereof to a second column portion so as to assure the continuity ofthe drilling column, said measuring element having on one portion of thelength thereof a predetermined section allowing for its deformation inat least one direction due to the action of the stresses applied to thedrilling column, said portion of the measuring element being providedwith detecting means for detecting these stresses, and telemeteringconductors connected to said detecting means and operatively associatedwith the drilling pipe, tubular safety element disposed coaxially withrespect to said measuring element, said measuring and safety elementsbeing joined together within each other with a play allowing for therelative displacement thereof during the deformation of the measuringelement, said safety element being rigidly secured at one of the endsthereof to one of said drilling column portions, and connecting meanslinking the second of the ends of said safety element to said measuringelement, said connecting means being adapted, during the deformation ofthe measuring element in said direction,

to limit he displaceme r t ao f said measuring element wit respect tosan s ety element to a maximum value, said safety element having apredetermined section capable of supporting the high stresses applied tothe drilling column when the relative displacement of said measuring andsafety elements has reached said maximum value.

2. A drilling column according to claim 1, wherein said connecting meanscomprises at least one pin joining together said measuring element andsaid safety element, at least one of said elements being adapted to havea limited displacement with respect to said pin.

3. A drilling column according to claim 1, wherein said connecting meansconsists of complementary threads provided respectively on saidmeasuring and safety elements, said threads joining together saidelements with a play allowing for a limited relative displacement ofsaid elements in at least one direction.

4. A drilling column according to claim 1, wherein said measuringelement is shielded from the influence of the difference of the staticpressure exerted by the drilling fluid between the internal wall and theexternal wall thereof by means of a tubular protecting element having athickness sufficient to withstand the pressure difference and coveringtightly at least one of the walls of said measuring element.

5. A drilling column according to claim 1, characterized by the assemblyin series of several measuring elements connected to at least one safetyelement by distinct connecting means, said measuring elements havingdifferent thicknesses whose deformation due to the effect of stresses islimited by said connecting means to values increasing with the thicknessof the measuring element.

* II i

1. A drilling column consisting of portions assembled end-toend,comprising in combination a deformable tubular measuring elementconnected at one end thereof to a first column portion and at the otherend thereof to a second column portion so as to assure the continuity ofthe drilling column, said measuring element having on one portion of thelength thereof a predetermined section allowing for its deformation inat least one direction due to the action of the stresses applied to thedrilling column, said portion of the measuring element being providedwith detecting means for detecting these stresses, and telemeteringconductors connected to said detecting means and operatively associatedwith the drilling pipe, a tubular safety element disposed coaxially withrespect to said measuring element, said measuring and safety elementsbeing joined together within each other with a play allowing for therelative displacement thereof during the deformation of the measuringelement, said safety element being rigidly secured at one of the endsthereof to one of said drilling column portions, and connecting meanslinking the second of the ends of said safety element to said measuringelement, said connecting means being adapted, during the deformation ofthe measuring element in said direction, to limit the displacement ofsaid measuring element with respect to said safety element to a maximumvalue, said safety element having a predetermined section capable ofsupporting the high stresses applied to the drilling column when therelative displacement of said measuring and safety elements has reachedsaid maximum value.
 2. A drilling column according to claim 1, whereinsaid connecting means comprises at least one pin joining together saidmeasuring element and said safety element, at least one of said elementsbeing adapted to have a limited displacement with respect to said pin.3. A drilling column according to claim 1, wherein said connecting meansconsists of complementary threads provided respectively on saidmeasuring and safety elements, said threads joining together saidelements with a play allowing for a limited relative displacement ofsaid elements in at least one direction.
 4. A drilling column accordingto claim 1, wherein said measuring element is shielded from theinfluence of the difference of the static pressure exerted by thedrilling fluid between the internal wall and the external wall thereofby means of a tubular protecting element having a thickness sufficientto withstand the pressure difference and covering tightly at least oneof the walls of said measuring element.
 5. A drilling column accordingto claim 1, characterized by the assembly in series of several measuringelements connected to at least one safety element by distinct connectingmeans, said measuring elements having different thicknesses whosedeformation due to the effect of stresses is limited by said connectingmeans to values increasing with the thickness of the measuring element.